The invention relates to an electrically insulated joint for metal pipes, comprising a metal receiving element including a bell and a metal insert element including a flange, wherein between the opposed surfaces of the flange and the bell a first insulating ring and an insulating elastic seal ring are compressed and between the rear surface of the flange and a pressure ring a second insulating ring is compressed. The pressure ring abuts the inner wall of the bell and is secured to the bell, wherein in the noncompressed state the inner diameter of the seal ring is smaller than the greatest outer diameter of the first insulating ring. At least in one of the opposed surfaces of the flange and the bell an annular recess is provided, which joins the passage of the respective element and of which the outer diameter is smaller than the outer diameter of the flange and in which the first insulating ring at least partially is received.
Such an electrically insulated joint is known from Dutch patent application No. 6819056. Though this joint represents a considerable improvement over the previously used electrically insulated joints, this joint still shows some disadvantages, which are mainly due to the fact that the insulating rings are composed of an insulating material of high compression strength. Such insulating material is more or less permeable for gas and liquid and upon getting old becomes brittle, scales and slowly but surely collapses under the mechanical and hydraulic stresses to which the insulated joint is subjected. The known joint, in particular does not withstand explosion tests. In the pipe lines including such joints, a relatively high pressure is present in normal operation, which may suddenly drop. The known electrically insulated joint thereby becomes defective in that the first insulating ring forcefully is pressed toward the interior of the joint.